1. Field of the Invention
The present invention relates to a signal vector quantizing apparatus and a speech analysis-synthesis system using the apparatus. The present invention particularly relates to a vector quantizing apparatus for high quality and low bit rate speech coding and a speech analysis-synthesis system for synthesizing high quality speech from a small amount of information, applied to low bit rate speech transmission, speech storage and forward, etc.
2. Description of the Prior Art
Heretofore, various methods have been proposed for efficient speech coding. For example, not only have various methods have been explained in an easy style but a large number of methods concerning waveform coding and information source coding (parameter coding) have been shown in the reading, by Kazuo Nakata, entitled "Digital Information Compression", Electronic Science Series 100, KOSAIDO SANPOU Co., Ltd., 1984.
On the other hand, heretofore, various methods have been proposed for speech analysis-synthesis. A so-called vocoder is a system particularly improved in information compressing rate. This is a system in which speech is separated into spectral envelope information and source information to be used as parameters. Typical examples of this system include a channel vocoder, an LPC (linear predictive coding) vocoder, a homomorphic vocoder, etc. The outlines thereof have been collected in the reading, by Sadaoki Furui, entitled "Digital Speech Processing", TOKAI UNIVERSITY PRESS, September 1985.
These methods are, however, insufficient in accuracy for extraction of a spectral envelope, so that a problem arises in the quality of synthesized speech.
On the contrary, a PSE (power spectral envelope) analysis-synthesis method has been proposed as a new spectral envelope extracting method recently. This is a method in which a spectral envelope is defined on the basis of a row of data obtained by sampling speech Fourier power spectra at intervals of a pitch frequency. The synthesized speech obtained by this method is high in quality compared with the conventional method. This method has been described in detail in the report, by Takayuki Nakajima et al., entitled "Power Spectral Envelope (PSE) Speech Analysis-Synthesis System", Acoustical Society of Japan, Vol. 44, No. 11, Sho. 63 (1988)-11.